The present invention relates to an internal combustion engine having a device for cyclically varying the speed of rotation of a cam for gas exchange control.
It is known in the state of the art to drive a cam for controlling an inlet or exhaust valve of an internal combustion engine by a rotary drive mechanism which causes the speed of rotation of a cam to vary in a cyclic manner about an average speed of rotation at a constant number of revolutions of the internal combustion engine. During each complete rotation of the cam a temporary increase of the angular velocity and a temporary decrease of the angular velocity occurs. The average angular velocity of the cam resulting thereof corresponds to the angular velocity of a cam of an internal combustion engine without cyclic variation of the angular velocity.
If the variation of the angular velocity of the cam is effected such that the increase of the speed of rotation of the cam occurs at a time during one rotation of said cam in which said cam operates the valve, the effective duration of opening of said valve is reduced. On the other hand, if the decrease of the speed of rotation occurs at a time of the rotation of said cam in which it operates the valve, a longer duration of opening of said valve is effected. By means of such mechanism it is possible to provide a variable timing of the opening of the valves of the internal combustion engine.
Such rotary drive mechanism is disclosed in the German patent application 195 01 172.4 which does not constitute a prior disclosure. The content of this prior German patent application shall be contained in the present application. In this internal combustion engine the cyclic variation of the speed of rotation of the cam is effected by a rotary drive mechanism comprising a first rotary body being disposed on a shaft and being fixed on said shaft so that it cannot rotate with respect to that shaft, a second rotary body being rotatably supported on said first rotary body and an intermediate member being rotatably supported in a plane perpendicular to the axis of rotation of said shaft and having a first sliding guide and a second sliding guide.
The rotation of the first rotary body is transmitted to the intermediate member by a first transmission element and said first sliding guide and from said intermediate member via the second sliding guide and a second transmission element to the second rotary body. If the intermediate member takes a position in which its axis of rotation is shifted with respect to the axis of rotation of the shaft so that it is not aligned with the latter, the second rotary body is cyclically rotated with respect to the first rotary body at one rotation of the shaft.
With a rotary drive mechanism of that kind either the rotation of the second rotary body can be transmitted to a cam for gas exchange control of an internal combustion engine, for instance by engaging gears, wherein in such case the cam is supported on a separate cam shaft, or the shaft can be formed as the cam shaft and the second rotary body as a cam for gas exchange control of an internal combustion engine.
In both cases there is provided an actuating member for supporting and shifting the intermediate member which supporting member partially accommodates the intermediate member from its outer side wherein said intermediate member with its circular outer circumferential surface is rotatably supported in a corresponding circular inner circumferential surface of the actuating member. The shifting of the actuating member and, accordingly, the intermediate member is effected via two eccentric elements which are engaged with the actuating member in a position outside the circular inner circumferential surface for supporting the intermediate member.
JP 5-118 208 A discloses a device for cyclically varying the speed of rotation of a cam for gas exchange control in which an intermediate ring serving to transmit the rotary motion is supported on a double eccentric assembly.